This invention relates to a spinneret assembly for subjecting two kinds of spinning liquids to composite spinning into composite fibers of sheath-and-core type.
Heretofore, a number of spinneret assemblies for producing composite fibers of sheath-and core type have been proposed, and a representative example thereof is disclosed in U.S. Pat. No. 2,987,797. According to the patent, the spinneret assembly is characterized in that it consists of a spinneret plate having spinning holes, and a back plate opposed thereto, with not so narrow a space being placed between these plates; a sheath component is distributed through the space over the whole of the spinneret; and the sheath component is radially introduced through the respective relatively narrow zones surrounding the respective inlets of spinning holes formed by circular flat projections provided concentric with the spinning holes on at least one of the plates.
The structure of such a spinneret assembly is readily applicable to a spinneret having a relatively small number of spinning holes sparsely arranged. However, if it is intended to densely arrange a large number of spinning holes, many manhours are required for precise cutting processing for providing the above circular projections, this resulting in a very expensive apparatus. Moreover, if the intervals between the spinning holes are narrowed, it may be practically impossible in some case to ensure room for providing the projections. Even if spinning holes are arranged at the points of intersection of square lattice, the minimum pitch is at least about 4 mm; hence it is difficult to raise the density of the spinning holes up to five holes/cm.sup.2 or more. Further, the spinneret of such a structure enables the sheath component to uniformly flow in the spinning holes from their periphery with the passage resistance of the sheath component caused by the above narrow zone; hence if the width of the ring-form projections is narrowed in order to densely arrange the spinning holes, the clearance between the spinneret plate and the back plate in the narrow zone must be made narrower. Thus, contaminative matters or gel-like substances contained in the spinning liquids are liable to clog in this clearance during spinning and hence obstruct a smooth flow of the sheath component to thereby make difficult a stable and long term spinning. Moreover, the above projections on the surface of the spinneret plate or the back plate are liable to be injured during cleaning or assembling operation thereof, which make the life of spinneret short. Thus the above structure have raised various problems.
An object of the present invention is to provide a spinneret assembly capable of spinning composite fibers which have a superior uniformity of fineness of single filaments, no composite unevenness and superior concentric properties, for a long term and in a stabilized manner, and also capable of corresponding to broad spinning conditions for various kinds of fiber raw materials. Another object of the present invention is to provide a spinneret assembly which is simple in structure and very easy in work, has a large number of spinning holes arranged over the whole surface of spinneret and also has a high productivity.
In view of the afore-mentioned present status of conventional spinnerets of sheath-and-core type composite fiber provided with a number of spinning holes, the present inventors have made extensive research, and as a result have found that when a spinneret assembly of a specific structure is devised, it is possible to make a spinneret assembly of composite fiber by an easy work and economically, which assembly can generally correspond to spinning conditions of various kinds of polymers; can reduce the degree of eccentricity of the core component; can reduce quality variation between single filaments; can reduce lapse of time; and can be provided with a large number or spinning holes close to each other.